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#include <bits/stdc++.h>

using namespace std;

int main() {
    ios_base::sync_with_stdio(0);
    int n, k; cin >> n >> k;
    vector<int> arr(n);
    for (int &v : arr) cin >> v;
    int ans = 0;
    for (int step = 0; step < n; ++step) {
        for (int i = 0; i < n; ++i) {
            if (i && arr[i - 1] - arr[i] > k) {
                ans += arr[i - 1] - k - arr[i];
                arr[i] = arr[i - 1] - k;
            }
            if (i < n - 1 && arr[i + 1] - arr[i] > k) {
                ans += arr[i + 1] - k - arr[i];
                arr[i] = arr[i + 1] - k;
            }
        }
    }
    cout << ans << "\n";
}